title: The organellar genome and metabolic potential of the hydrogen-producing mitochondrion of Nyctotherus ovalis.
abstract: It is generally accepted that hydrogenosomes (hydrogen-producing organelles) evolved from a mitochondrial ancestor. However, until recently, only indirect evidence for this hypothesis was available. Here, we present the almost complete genome of the hydrogen-producing mitochondrion of the anaerobic ciliate Nyctotherus ovalis and show that, except for the notable absence of genes encoding electron transport chain components of Complexes III, IV, and V, it has a gene content similar to the mitochondrial genomes of aerobic ciliates. Analysis of the genome of the hydrogen-producing mitochondrion, in combination with that of more than 9,000 genomic DNA and cDNA sequences, allows a preliminary reconstruction of the organellar metabolism. The sequence data indicate that N. ovalis possesses hydrogen-producing mitochondria that have a truncated, two step (Complex I and II) electron transport chain that uses fumarate as electron acceptor. In addition, components of an extensive protein network for the metabolism of amino acids, defense against oxidative stress, mitochondrial protein synthesis, mitochondrial protein import and processing, and transport of metabolites across the mitochondrial membrane were identified. Genes for MPV17 and ACN9, two hypothetical proteins linked to mitochondrial disease in humans, were also found. The inferred metabolism is remarkably similar to the organellar metabolism of the phylogenetically distant anaerobic Stramenopile Blastocystis. Notably, the Blastocystis organelle and that of the related flagellate Proteromonas lacertae also lack genes encoding components of Complexes III, IV, and V. Thus, our data show that the hydrogenosomes of N. ovalis are highly specialized hydrogen-producing mitochondria.
authors.affiliation: Department of Evolutionary Microbiology, Institute for Water and Wetland Research, Radboud University Nijmegen, Nijmegen, The Netherlands.
authors.forename: Rob M
authors.initials: RM
authors.lastname: de Graaf
authors.forename: Guenola
authors.initials: G
authors.lastname: Ricard
authors.forename: Theo A
authors.initials: TA
authors.lastname: van Alen
authors.forename: Isabel
authors.initials: I
authors.lastname: Duarte
authors.forename: Bas E
authors.initials: BE
authors.lastname: Dutilh
authors.forename: Carola
authors.initials: C
authors.lastname: Burgtorf
authors.forename: Jan W P
authors.initials: JW
authors.lastname: Kuiper
authors.forename: Georg W M
authors.initials: GW
authors.lastname: van der Staay
authors.forename: Aloysius G M
authors.initials: AG
authors.lastname: Tielens
authors.forename: Martijn A
authors.initials: MA
authors.lastname: Huynen
authors.forename: Johannes H P
authors.initials: JH
authors.lastname: Hackstein
mesh_terms: D005075:Biological Evolution; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D016798:Ciliophora / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D022761:Gene Transfer, Horizontal; D017125:Genes, Protozoan / Q000235:genetics; D054629:Genome, Mitochondrial / Q000235:genetics*; D006859:Hydrogen / Q000378:metabolism*; D008928:Mitochondria / Q000235:genetics* / Q000378:metabolism*; D015388:Organelles / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D015800:Protozoan Proteins; D006859:Hydrogen